I have a working zimbra install on centos 5 64 bit. I just got done with it yesterday after getting local BIND to work on it for DNS resolution to the local ip.
Mail routing is working in and out just fine.
What I'm having a difficult time grasping is why I can send to my mail domain from the outside world and it works when the MX record for my mail domain is local? How does Gmail know that my mail domain exists when it can't query the mx record?
I'm not saying anything is broken, this is the way I want my install to work, but I want to understand why something works the way it does...